1. Field of the Invention
The present invention relates to a so-called front-opening interface mechanical standard (FIMS) system used when, in a semiconductor manufacturing process or the like, contained objects (objects to be stored) including wafers, which are retained inside transfer containers called pods, are transferred between semiconductor processing apparatuses, and relates to an object to be stored transfer system in which the objects to be stored are transferred between semiconductor processing apparatuses or the like. In particular, the present invention relates to an object to be stored (wafer) transfer system including a FIMS system in which pods which are so-called front-opening unified pods (FOUP) serving as sealed containers for housing wafers are mounted and lids of the pods are opened/closed so as to transport the wafers to the pods, and a transfer chamber which is a mini-environment connected to the FIMS system and in which a robot for transporting the wafers needs to be provided.
2. Description of the Related Art
Up to now, a semiconductor manufacturing process has been conducted in a so-called clean chamber in which semiconductor wafers are treated with high cleanliness maintained therein. However, in order to cope with an increase in wafer size and to reduce a cost necessary for maintenance of the clean chamber, a method of maintaining only the following in a highly clean state is employed in recent years, an inside of a processing apparatus, the pod (container of wafer), and a mini-environment in which a transporting robot for transferring the wafer from the pod to the processing apparatus is housed.
The pod includes a substantially cubic body having a rack capable of retaining multiple wafers therein in a state in which the wafers are separated from each other in parallel and having an opening which is used for putting in/taking out wafers on one of surfaces constituting an outer surface, and a lid for closing the opening. A pod in which a surface provided with the opening is located not on a bottom surface of the pod but on a side surface of the pod (in front of the mini-environment) is collectively referred to as a front-opening unified pod (FOUP). The present invention is mainly intended for a structure using the FOUP.
The above-mentioned mini-environment includes a first opening portion faced with the opening of the pod, a door for closing the first opening portion, a processing-equipment-side second opening portion which is provided on the semiconductor processing equipment side, a transporting robot which intrudes from the first opening portion to the inside of the pod for retaining the wafer and passes and transfers the wafer through the processing-equipment-side second opening portion to the processing equipment side. Simultaneously, the structure forming the mini-environment includes a placing base for supporting the pod such that the pod opening portion is opposed to the front of the door.
On the upper surface of the placing base, there are arranged a positioning pin which is fitted to a hole for positioning provided in the lower surface of the pod so as to define the placing position of the pod, and a clamping unit which is engaged with a clamped portion provided in the lower surface of the pod so as to secure the pod with respect to the placing base. Normally, the placing base is movable back and forth with respect to a door direction by a predetermined distance. When the wafers in the pod are transported to the processing equipment, the pod is moved in a state of being placed until the lid of the pod is brought into contact with the door. After that contact, the lid is removed from the opening of the pod by the door. With those operations, the inside of the pod and the inside of the processing equipment are communicated with each other through an intermediation of the mini-environment. Subsequently, a wafer transporting operation is repeated. A system including the placing base, the door, the first opening portion, a door opening/closing mechanism, a wall which constitutes a part of the mini-environment including the first opening portion is collectively referred to as a front-opening interface mechanical standard (FIMS) system.
In this case, the inside of the pod in a state of containing wafers or the like is normally filled with dry nitrogen or the like which is controlled in a highly clean state, and hence contaminants, an oxidized gas, and the like are prevented from intruding to the inside of the pod. However, when the wafers in the pod are brought into various processing apparatuses so as to undergo a predetermined process, the inside of the pod and the inside of the processing equipment are constantly communicated with each other. In the structure as described above, which is exemplified in Japanese Patent Application Laid-Open No. 2006-019726, the fan and the filter are arranged in the upper portion of the chamber in which the transporting robot is arranged, and the clean air which has undergone particle control is normally introduced to the inside of the chamber. However, when the air as described above intrudes to the inside of the pod, there is a risk that oxygen and moisture in the air oxidize the surface of the wafer.
In accordance with the development of smaller and higher-performance semiconductor devices, consideration is started to be given on oxidization caused by oxygen and the like which intrudes to the inside of the pod, which has not conventionally constituted a serious problem. Those oxidized gases form extremely thin oxide films on the surface of the wafer or the layers of various types formed on the wafer. Owing to the existence of the oxide films as described above, there arises a risk that desired properties cannot be ensured in ultra-small semiconductor devices. As a countermeasure therefor, it is probable that the gas which has not undergone control on an oxygen partial pressure is prevented from intruding from the outside of the pod to the inside of the pod. Specifically, Japanese Patent Application Laid-Open No. 2003-045933 discloses a structure in which a supply nozzle and a suction nozzle for the gases are provided in a region adjacent to an opening of the pod in a FIMS system so as to form an airflow film which substantially close the opening of the pod. The airflow film thus formed prevents the external air from intruding to the inside of the pod.
However, with respect to the so-called mini-environment in which the transporting robot is arranged, normal air which has merely undergone control on dust and the like is supplied through an intermediation of the filter. Accordingly, when the wafers are conveyed out of the pod or when conveyed into the pod, the wafers constantly pass the environment which has not undergone oxide gas control. Actually, the transfer operation is performed within an extremely short period of time, and hence does not constitute a serious problem in the present semiconductor manufacturing process. However, in a phenomenon such as dew condensation, moisture and the like can adhere to the surfaces of the wafers even within a short period of time. In addition, it is difficult to suppress the oxidation of various thin films once moisture and the like adhere thereto.